When photographing a scene, light rays emitted from objects within the scene are recorded on a film such as regular film or digital film. Hence, photography involves the recording of these light rays. When lighting conditions are improper (e.g., when photographing in low light), pictures lack some of the scene information when compared with pictures taken in sufficient lighting conditions.
Taking satisfactory photos under dim lighting conditions has historically posed a very difficult problem. Often, the images are blurred and/or underexposed. Underexposures generally results from not exposing the film to sufficient amounts of light. Underexposure may be somewhat corrected by exposing the film for a longer period, for example, by using a lower shutter speed to keep the shutter open for a longer period. Lower shutter speed, however, results in blurring. The blurring problem is exasperated when using a hand-held camera (e.g., rather than a tripod), in part, because of the increased movement during shutter openings. Blurring may also occur due to movement of the objects within the scene during shutter openings.
A couple of common solutions include use of flashes (to compensate for low lighting by introducing additional lighting) or a film with higher ISO (a prefix set by the International Organization for Standardization).
Using flashes is limiting for a variety of reasons. For example, flashes are only operational over relatively short distances. Also, flashes may result in change of colors, yielding an inaccurate representation of the scene. Multiple flashes (e.g., with remote activation) may be utilized to improve the results of flash photography, but setting up several flashes around a scene may not always be feasible (e.g., in outdoor photography or when capturing shots with short notice).
Higher ISO film is also limiting for a number of reasons. In traditional photography, the film is often only changeable one roll at a time. Accordingly, when a camera is loaded with higher ISO film (e.g., suitable for low lighting conditions), the camera can not be used for normal lighting conditions without limiting the photographers options (e.g., where pictures have to be taken at higher shutter speeds to avoid overexposure). In digital photography, the performance of higher ISO settings entirely depends on the camera sensor, which can significantly vary between different cameras. Moreover, an even more important shortcoming is the relatively higher amount of noise that results from using the higher ISO.
Currently, there are several techniques for improving the quality of blurred images, e.g., resulting from an exposure time above the safe shutter speed. Generally, the safe shutter speed is a speed no slower than the reciprocal of the focal length of the lens. These techniques can be roughly classified into in-process and post-process approaches which limit motion blur due to, for example, a long exposure time, camera shake, or object movement.
In-process approaches are mainly hardware-based techniques, where lens stabilization is achieved by camera shake compensation. Alternatively, high-speed digital cameras (such as those with complementary metal oxide semiconductor (CMOS) sensors) can perform high-speed frame captures within normal exposure time which allows for multiple image-based motion blur restoration. The in-process techniques are able to produce relatively clear and crisp images, given a reasonable exposure time. However, they require specially designed hardware devices.
On the other hand, post-process methods can be generally considered as motion deblurring techniques. Among them, blind deconvolution is widely adopted to enhance a single blurred image, which may be applied under different assumptions on the point spread function (PSF). Alternatively, several images with different blurring directions or an image sequence can be used, in more general situations, to estimate the PSF. In both cases, due to the discretization and quantization of images in both spatial and temporal coordinates, the PSF can not be reliably estimated, which produces a result inferior to the ground truth image (which is an image either taken with a camera on a tripod or of a static scene with correct exposure). A hybrid imaging system consisting of a primary (high spatial resolution) detector and a secondary (high temporal resolution) detector has also been proposed. The secondary detector provides more accurate motion information to estimate the PSF; thus, making deblurring possible even under long exposure. However, this technique needs additional hardware support, and the deblurred images are still not visibly as good as the ground truth in detail.
Accordingly, the present solutions fail to provide sufficient image quality.